This paper presents the design and testing of a novel rotary transformer for rotary ultrasonic machining (RUM). The transformer structure is innovatively designed for easy assembly and disassembly, which provides increased convenience to tool replacement in RUM. Circuit analysis shows the efficiency loss caused by the structure simplification is less than 5%. Also, the effect of the primary core angle and air gap length on coupling coefficient is studied for guiding the design. A rotary transformer with 90° primary core and 1.0 mm air gap is achieved. Contrast tests were carried out in simulation and experiment. Results show this novel rotary transformer transmission efficiency is 0.8972, which is agree with the theoretical value.